Motorcycle: Twins - JH, JDH Two - Cam, 1928 - 1929
Date: Sunday, October 31 @ 23:04:33 UTC
Topic: Motorcycle, Motorcycles, Motor Cycle
JH, JDH Two - Cam, 1928 - 1929
Twin-cam and even eight-valve machines had formed the cutting edge of Harley-Davidson's official racing efforts since the First World War, yet the ordinary road-going motorcyclist could only dream of such performance. All that changed in 1928 when Harley offered a two-cam motorcycle to the general public at an affordable price. These special J-series machines were available for two years only, as the 61-inch JH and the awesome 74-inch JDH, which were priced at $360 and $370 respectively.
"The magic words 'two-cam' mean exceptional speed and power," extolled contemporary advertisements, with some justification. Not for the last time, Milwaukee was treading the fine line between effective salesmanship and encouraging public disquiet over bad boys on antisocial machines.
Both twin-cam engines featured inlet-over-exhaust valve operation driven by paired, gear-driven cams in a timing case on the right side of the engine. Instead of operating via Harley-Davidson's customary roller arms, the cam lobes acted directly on tappets, offering more accurate valve control, higher revs and improved combustion. The height of each cylinder's inlet valve necessitated flamboyant clearance cutaways in the narrow fuel tank, which gave the "JH" its characteristically racy appearance.
The two engines differed in both bore and stroke, as well as in the use of Dow metal pistons, but were built on essentially the same crankcases. These were connected by roller primary chain to a multi-plate dry clutch and three-speed gearbox, which in turn drove the rear wheel by chain.
As well as the choice of capacities, two specifications of the Two-Cam were offered, although numerous racing specials would be created in private hands. As well as the competitive potential of stripped-down Model Js, Juneau Avenue anticipated a demand for an exclusive road version — or "superbike" as it might be known today. Thus the Two-Cam was available with full electrical equipment, carburettor air cleaner, fully valanced mudguards and front and rear brakes.
Echoes of the machine's racing pedigree were retained, however, in the slimline "sport" chassis, single seat and racer-style two-gallon (7.5 litre) fuel tank. Even as a roadster, the Two-Cam was billed as "the fastest model ever offered by Harley-Davidson" with the JDH specially recommended "for greatest speed and maximum performance."
With an 80-inch version available on special order in 1929, this olive green projectile was no less than the American equivalent of Brough Superior's sensational SS100 in Europe. Yet even this degree of exclusivity was priced too high for an American market more interested in cars, and the Two-Cams passed into legend after spending a very short two years in the Harley-Davidson range.
Engine: 2-cam, F-head V-twin
Capacity: 60.33cu in (988cc) or 74.2 cu in (1,216cc)
Wheelbase: 60in (1,525mm)
Top speed: around 85mph (137kph)
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